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This autosomal recessive disorder is designated Meckel syndrome type 7 (MKS7) based on the classic phenotypic triad of (1) cystic renal disease; (2) a central nervous system abnormality, and (3) hepatic abnormalities, as defined by Meckel (1822), Salonen (1984), and Logan et al. (2011). According to these criteria, polydactyly is a variable feature. Herriot et al. (1991) and Al-Gazali et al. (1996) concluded that Dandy-Walker malformation can be the phenotypic manifestation of a central nervous system malformation in MKS. For a general phenotypic description and a discussion of genetic heterogeneity of Meckel syndrome, see MKS1 (249000). [from OMIM]

Isolated gonadotropin-releasing hormone (GnRH) deficiency (IGD) is characterized by inappropriately low serum concentrations of the gonadotropins LH (luteinizing hormone) and FSH (follicle-stimulating hormone) in the presence of low circulating concentrations of sex steroids. IGD is associated with a normal sense of smell (normosmic IGD) in approximately 40% of affected individuals and an impaired sense of smell (Kallmann syndrome) in approximately 60%. IGD can first become apparent in infancy, adolescence, or adulthood. Infant boys with congenital IGD often have micropenis and cryptorchidism. Adolescents and adults with IGD have clinical evidence of hypogonadism and incomplete sexual maturation on physical examination. Adult males with IGD tend to have prepubertal testicular volume (i.e., <4 mL), absence of secondary sexual features (e.g., facial and axillary hair growth, deepening of the voice), decreased muscle mass, diminished libido, erectile dysfunction, and infertility. Adult females have little or no breast development and primary amenorrhea. Although skeletal maturation is delayed, the rate of linear growth is usually normal except for the absence of a distinct pubertal growth spurt. [from GeneReviews]

Brugada syndrome is characterized by cardiac conduction abnormalities (ST segment abnormalities in leads V1-V3 on EKG and a high risk for ventricular arrhythmias) that can result in sudden death. Brugada syndrome presents primarily during adulthood, although age at diagnosis may range from infancy to late adulthood. The mean age of sudden death is approximately 40 years. Clinical presentations may also include sudden infant death syndrome (SIDS; death of a child during the first year of life without an identifiable cause) and sudden unexpected nocturnal death syndrome (SUNDS), a typical presentation in individuals from Southeast Asia. Other conduction defects can include first-degree AV block, intraventricular conduction delay, right bundle branch block, and sick sinus syndrome. [from GeneReviews]

Hypertrophic cardiomyopathy is a heart condition characterized by thickening (hypertrophy) of the heart (cardiac) muscle. When multiple members of a family have the condition, it is known as familial hypertrophic cardiomyopathy. Hypertrophic cardiomyopathy also occurs in people with no family history; these cases are considered nonfamilial hypertrophic cardiomyopathy. 

Nonfamilial hypertrophic cardiomyopathy tends to be milder. This form typically begins later in life than familial hypertrophic cardiomyopathy, and affected individuals have a lower risk of serious cardiac events and sudden death than people with the familial form.

In familial hypertrophic cardiomyopathy, cardiac thickening usually occurs in the interventricular septum, which is the muscular wall that separates the lower left chamber of the heart (the left ventricle) from the lower right chamber (the right ventricle). In some people, thickening of the interventricular septum impedes the flow of oxygen-rich blood from the heart, which may lead to an abnormal heart sound during a heartbeat (heart murmur) and other signs and symptoms of the condition. Other affected individuals do not have physical obstruction of blood flow, but the pumping of blood is less efficient, which can also lead to symptoms of the condition. Familial hypertrophic cardiomyopathy often begins in adolescence or young adulthood, although it can develop at any time throughout life.

The symptoms of familial hypertrophic cardiomyopathy are variable, even within the same family. Many affected individuals have no symptoms. Other people with familial hypertrophic cardiomyopathy may experience chest pain; shortness of breath, especially with physical exertion; a sensation of fluttering or pounding in the chest (palpitations); lightheadedness; dizziness; and fainting.

While most people with familial hypertrophic cardiomyopathy are symptom-free or have only mild symptoms, this condition can have serious consequences. It can cause abnormal heart rhythms (arrhythmias) that may be life threatening. People with familial hypertrophic cardiomyopathy have an increased risk of sudden death, even if they have no other symptoms of the condition. A small number of affected individuals develop potentially fatal heart failure, which may require heart transplantation. [from MedlinePlus Genetics]

Parkinson's disease is a progressive disorder of the nervous system. The disorder affects several regions of the brain, especially an area called the substantia nigra that controls balance and movement.

Often the first symptom of Parkinson's disease is trembling or shaking (tremor) of a limb, especially when the body is at rest. Typically, the tremor begins on one side of the body, usually in one hand. Tremors can also affect the arms, legs, feet, and face. Other characteristic symptoms of Parkinson's disease include rigidity or stiffness of the limbs and torso, slow movement (bradykinesia) or an inability to move (akinesia), and impaired balance and coordination (postural instability). These symptoms worsen slowly over time.

Parkinson's disease can also affect emotions and thinking ability (cognition). Some affected individuals develop psychiatric conditions such as depression and visual hallucinations. People with Parkinson's disease also have an increased risk of developing dementia, which is a decline in intellectual functions including judgment and memory.

Generally, Parkinson's disease that begins after age 50 is called late-onset disease. The condition is described as early-onset disease if signs and symptoms begin before age 50. Early-onset cases that begin before age 20 are sometimes referred to as juvenile-onset Parkinson's disease. [from MedlinePlus Genetics]

Congenital muscular dystrophy-dystroglycanopathy with brain and eye anomalies (type A), which includes both the more severe Walker-Warburg syndrome (WWS) and the slightly less severe muscle-eye-brain disease (MEB), is an autosomal recessive disorder with characteristic brain and eye malformations, profound mental retardation, congenital muscular dystrophy, and death usually in the first years of life. It represents the most severe end of a phenotypic spectrum of similar disorders resulting from defective glycosylation of alpha-dystroglycan (DAG1; 128239), collectively known as 'dystroglycanopathies' (summary by Roscioli et al., 2012). For a general phenotypic description and a discussion of genetic heterogeneity of muscular dystrophy-dystroglycanopathy type A, see MDDGA1 (236670). [from OMIM]

Most characteristically, Aicardi-Goutières syndrome (AGS) manifests as an early-onset encephalopathy that usually, but not always, results in severe intellectual and physical disability. A subgroup of infants with AGS present at birth with abnormal neurologic findings, hepatosplenomegaly, elevated liver enzymes, and thrombocytopenia, a picture highly suggestive of congenital infection. Otherwise, most affected infants present at variable times after the first few weeks of life, frequently after a period of apparently normal development. Typically, they demonstrate the subacute onset of a severe encephalopathy characterized by extreme irritability, intermittent sterile pyrexias, loss of skills, and slowing of head growth. Over time, as many as 40% develop chilblain skin lesions on the fingers, toes, and ears. It is becoming apparent that atypical, sometimes milder, cases of AGS exist, and thus the true extent of the phenotype associated with pathogenic variants in the AGS-related genes is not yet known. [from GeneReviews]

Autosomal dominant epilepsy with auditory features (ADEAF) is a focal epilepsy syndrome with auditory symptoms and/or receptive aphasia as prominent ictal manifestations. The most common auditory symptoms are simple unformed sounds including humming, buzzing, or ringing; less common forms are distortions (e.g., volume changes) or complex sounds (e.g., specific songs or voices). Ictal receptive aphasia consists of a sudden onset of inability to understand language in the absence of general confusion. Less commonly, other ictal symptoms may occur, including sensory symptoms (visual, olfactory, vertiginous, or cephalic) or motor, psychic, and autonomic symptoms. Most affected individuals have focal to bilateral tonic-clonic seizures, usually accompanied by "focal aware" and "focal impaired-awareness" seizures, with auditory symptoms as a major focal aware seizure manifestation. Some persons have seizures precipitated by sounds such as a ringing telephone. Age at onset is usually in adolescence or early adulthood (range: age 4-50 years). The clinical course of ADEAF is benign. Seizures are usually well controlled after initiation of medical therapy. [from GeneReviews]

Cone-rod dystrophy is a group of related eye disorders that causes vision loss, which becomes more severe over time. These disorders affect the retina, which is the layer of light-sensitive tissue at the back of the eye. In people with cone-rod dystrophy, vision loss occurs as the light-sensing cells of the retina gradually deteriorate.

The first signs and symptoms of cone-rod dystrophy, which often occur in childhood, are usually decreased sharpness of vision (visual acuity) and increased sensitivity to light (photophobia). These features are typically followed by impaired color vision (dyschromatopsia), blind spots (scotomas) in the center of the visual field, and partial side (peripheral) vision loss. Over time, affected individuals develop night blindness and a worsening of their peripheral vision, which can limit independent mobility. Decreasing visual acuity makes reading increasingly difficult and most affected individuals are legally blind by mid-adulthood. As the condition progresses, individuals may develop involuntary eye movements (nystagmus).

There are more than 30 types of cone-rod dystrophy, which are distinguished by their genetic cause and their pattern of inheritance: autosomal recessive, autosomal dominant, and X-linked. Additionally, cone-rod dystrophy can occur alone without any other signs and symptoms or it can occur as part of a syndrome that affects multiple parts of the body. [from MedlinePlus Genetics]

Tetrahydrobiopterin deficiency is a rare disorder characterized by a shortage (deficiency) of a molecule called tetrahydrobiopterin or BH4. This condition alters the levels of several substances in the body, including phenylalanine. Phenylalanine is a building block of proteins (an amino acid) that is obtained through the diet. It is found in foods that contain protein and in some artificial sweeteners. High levels of phenylalanine are present from early infancy in people with untreated tetrahydrobiopterin deficiency. This condition also alters the levels of chemicals called neurotransmitters, which transmit signals between nerve cells in the brain.

Infants with tetrahydrobiopterin deficiency appear normal at birth, but medical problems ranging from mild to severe become apparent over time. Signs and symptoms of this condition can include intellectual disability, progressive problems with development, movement disorders, difficulty swallowing, seizures, behavioral problems, and an inability to control body temperature. [from MedlinePlus Genetics]

FBLN5-related cutis laxa is characterized by cutis laxa, early childhood-onset pulmonary emphysema, peripheral pulmonary artery stenosis, and other evidence of a generalized connective disorder such as inguinal hernias and hollow viscus diverticula (e.g., intestine, bladder). Occasionally, supravalvar aortic stenosis is observed. Intrafamilial variability in age of onset is observed. Cardiorespiratory failure from complications of pulmonary emphysema (respiratory or cardiac insufficiency) is the most common cause of death. [from GeneReviews]

Lynch syndrome-4 (LYNCH4), or hereditary nonpolyposis colorectal cancer type 4 (HNPCC4), is an autosomal dominant disorder characterized primarily by the development of early-onset colorectal cancer. It is associated with the development of a variety of epithelial tumors that include endometrial cancer, stomach cancer, and ovarian cancer (summary by Thompson et al., 2004). [from OMIM]

EZH2-related overgrowth includes EZH2-related Weaver syndrome at one end of the spectrum and tall stature at the other. Although most individuals diagnosed with a heterozygous EZH2 pathogenic variant have been identified because of a clinical suspicion of Weaver syndrome, a minority have been identified through molecular genetic testing of family members of probands or individuals with overgrowth who did not have a clinical diagnosis of Weaver syndrome. Thus, the extent of the phenotypic spectrum associated with a heterozygous EZH2 pathogenic variant is not yet known. Weaver syndrome is characterized by tall stature, variable intellect (ranging from normal intellect to severe intellectual disability), characteristic facial appearance, and a range of associated clinical features including advanced bone age, poor coordination, soft doughy skin, camptodactyly of the fingers and/or toes, umbilical hernia, abnormal tone, and hoarse low cry in infancy. Brain MRI has identified abnormalities in a few individuals with EZH2-related overgrowth. Neuroblastoma occurs at a slightly increased frequency in individuals with a heterozygous EZH2 pathogenic variant but data are insufficient to determine absolute risk. There is currently no evidence that additional malignancies (including hematologic malignancies) occur with increased frequency. [from GeneReviews]

Rupture of an intracranial aneurysm, an outpouching or sac-like widening of a cerebral artery, leads to a subarachnoid hemorrhage, a sudden-onset disease that can lead to severe disability and death. Several risk factors such as smoking, hypertension, and excessive alcohol intake are associated with subarachnoid hemorrhage (summary by Krischek and Inoue, 2006). For a discussion of genetic heterogeneity of intracranial berry aneurysm, see ANIB1 (105800). [from OMIM]

Preaxial polydactyly II (PPD2) is a limb malformation in which duplication, full or partial, of the first digital ray of hands or feet results in extra digits. Triphalangeal thumb is characterized by the presence of 3 phalanges within the thumb. The extra middle phalanx may be fully formed, trapezoidal, or a small triangular 'delta' phalanx; the thumb may be opposable or nonopposable. Preaxial polydactyly and triphalangeal thumb may cosegregate, or each occur in isolation, within families with mutation in the zone of polarizing activity (ZPA) regulatory sequence (ZRS), a regulatory element for the SHH gene (600725) that is contained within intron 5 of the LMBR1 gene (Heutink et al., 1994; Furniss et al., 2008; VanderMeer et al., 2014). [from OMIM]

Distal hereditary motor neuronopathy (dHMN or HMN) is a heterogeneous group of neuromuscular disorders caused by anterior horn cell degeneration and characterized by progressive distal motor weakness and muscular atrophy of the peripheral nervous system without sensory impairment. Distal HMN is also referred to as spinal Charcot-Marie-Tooth disease (spinal CMT). Distal HMN is often referred to as a 'neuronopathy' instead of a 'neuropathy' based on the hypothesis that the primary pathologic process resides in the neuron cell body and not in the axons (Irobi et al., 2006). Historically, Harding (1993) proposed a clinical classification of distal HMN into 7 phenotypic subtypes according to age at onset, mode of inheritance, and presence of additional features; see NOMENCLATURE. Genetic Heterogeneity of Autosomal Dominant Distal Hereditary Motor Neuronopathy Genetically distinct forms of autosomal dominant distal hereditary motor neuropathy include HMND1; HMND2 (158590), caused by mutation in the HSPB8 gene (608014); HMND3 (608634), caused by mutation in the HSPB1 gene (602195); HMND4 (613376), caused by mutation in the HSPB3 gene (604624); HMND5 (600794), caused by mutation in the GARS gene (600287); HMND6 (615575), caused by mutation in the FBXO38 gene (608533); HMND7 (158580), caused by mutation in the SLC5A7 gene (608761); HMND8 (600175), caused by mutation in the TRPV4 gene (605427); HMND9 (617721), caused by mutation in the WARS gene (191050); HMND10 (620080), caused by mutation in the EMILIN1 gene (130660); HMND11 (620528), caused by mutation in the SPTAN1 gene (182810); HMND12 (614751), caused by mutation in the REEP1 gene (609139); HMND13 (619112), caused by mutation in the BSCL2 gene (606158); and HMND14 (607641), caused by mutation in the DCTN1 gene (601143). See also X-linked HMN (HMNX; 300489), caused by mutation in the ATP7A gene (300011) on chromosome Xq21. Additional disorders with overlapping features include autosomal dominant ALS4 (602433), caused by mutation in the SETX gene (608465); and CMS7A (616040), caused by mutation in the SYT2 gene (600104). [from OMIM]

Deficiency of antithrombin III is a major risk factor for venous thromboembolic disease. Two categories of AT-III deficiency have been defined on the basis of AT-III antigen levels in the plasma of affected individuals. The majority of AT-III deficiency families belong in the type I (classic) deficiency group and have a quantitatively abnormal phenotype in which antigen and heparin cofactor levels are both reduced to about 50% of normal. The second category of AT-III deficiency has been termed type II (functional) deficiency. Affected individuals from these kindreds produce dysfunctional AT-III molecules; they have reduced heparin cofactor activity levels (about 50% of normal) but levels of AT-III antigen are often normal or nearly normal (summary by Bock and Prochownik, 1987). The 2 categories of antithrombmin III deficiency have been classified further. Type I (low functional and immunologic antithrombin) has been subdivided into subtype Ia (reduced levels of normal antithrombin), and type Ib (reduced levels of antithrombin and the presence of low levels of a variant). Type II (low functional but normal immunologic antithrombin) has been subdivided into subtype IIa (functional abnormalities affecting both the reactive site and the heparin-binding site of AT3); subtype IIb (functional abnormalities limited to the reactive site); and subtype IIc (functional abnormalities limited to the heparin-binding site) (summary by Lane et al., 1992). [from OMIM]

Brunelli et al. (1996) described schizencephaly as an extremely rare congenital disorder characterized by a full-thickness cleft within the cerebral hemispheres. The clefts are lined with gray matter and most commonly involve the parasylvian regions (Wolpert and Barnes, 1992). Large portions of the cerebral hemispheres may be absent and replaced by cerebrospinal fluid. Two types of schizencephaly have been described, depending on the size of the area involved and the separation of the cleft lips (Wolpert and Barnes, 1992). Type I schizencephaly consists of a fused cleft. This fused pial-ependymal seam forms a furrow in the developing brain, and is lined by polymicrogyric gray matter. In type II schizencephaly, there is a large defect, a holohemispheric cleft in the cerebral cortex filled with fluid and lined by polymicrogyric gray matter. The clinical manifestations depend on the severity of the lesion. Patients with type I are often almost normal; they may have seizures and spasticity. In type II abnormalities, there is usually mental retardation, seizures, hypotonia, spasticity, inability to walk or speak, and blindness. Schizencephaly may be part of the larger phenotypic spectrum of holoprosencephaly (HPE; see 236100). [from OMIM]

Autosomal dominant epilepsy with auditory features (ADEAF) is a focal epilepsy syndrome with auditory symptoms and/or receptive aphasia as prominent ictal manifestations. The most common auditory symptoms are simple unformed sounds including humming, buzzing, or ringing; less common forms are distortions (e.g., volume changes) or complex sounds (e.g., specific songs or voices). Ictal receptive aphasia consists of a sudden onset of inability to understand language in the absence of general confusion. Less commonly, other ictal symptoms may occur, including sensory symptoms (visual, olfactory, vertiginous, or cephalic) or motor, psychic, and autonomic symptoms. Most affected individuals have focal to bilateral tonic-clonic seizures, usually accompanied by "focal aware" and "focal impaired-awareness" seizures, with auditory symptoms as a major focal aware seizure manifestation. Some persons have seizures precipitated by sounds such as a ringing telephone. Age at onset is usually in adolescence or early adulthood (range: age 4-50 years). The clinical course of ADEAF is benign. Seizures are usually well controlled after initiation of medical therapy. [from GeneReviews]

The signs and symptoms of myofibrillar myopathy vary widely among affected individuals, typically depending on the condition's genetic cause. Most people with this disorder begin to develop muscle weakness (myopathy) in mid-adulthood. However, features of this condition can appear anytime between infancy and late adulthood. Muscle weakness most often begins in the hands and feet (distal muscles), but some people first experience weakness in the muscles near the center of the body (proximal muscles). Other affected individuals develop muscle weakness throughout their body. Facial muscle weakness can cause swallowing and speech difficulties. Muscle weakness worsens over time.

Other signs and symptoms of myofibrillar myopathy can include a weakened heart muscle (cardiomyopathy), muscle pain (myalgia), loss of sensation and weakness in the limbs (peripheral neuropathy), and respiratory failure. Individuals with this condition may have skeletal problems including joint stiffness (contractures) and abnormal side-to-side curvature of the spine (scoliosis). Rarely, people with this condition develop clouding of the lens of the eyes (cataracts).

Myofibrillar myopathy is part of a group of disorders called muscular dystrophies that affect muscle function and cause weakness. Myofibrillar myopathy primarily affects skeletal muscles, which are muscles that the body uses for movement. In some cases, the heart (cardiac) muscle is also affected. [from MedlinePlus Genetics]